The present invention relates generally to a method of regulating the tension of warp yarns in a weaving machine. More specifically, it relates to a method of regulating the tension of warp yarns in a loom by controlling the feeding speed of the warp yarns from a warp beam in response to the displacement of a tension roller beyond a predetermined permissible range of warp tension or with a rapid rate of displacement thereof.
In a conventional method of regulating the warp yarns delivered from a warp beam in a weaving machine so as to maintain the tension thereof within the limits of a predetermined permissible range, the variation of the warp yarn tension is monitored constantly by a detecting member such as a tension roller movable with a change in the tension of the warps, and the speed at which the warp yarns are unwound from the warp beam is increased when the tension is built up to exceed the upper limit of the permissible range while the speed is decreased when the tension is dropped below the lower limit of the range, thus providing automatic regulation of warp yarn tension during the weaving operation of the loom.
A typical arrangement for controlling the warp yarn tension in a weaving machine or a loom is exemplified in FIG. 1. A tension roller 1 which is attached at one end of a tension lever 4 rotatable about a stationary shaft 30 is caused to move up and down in response to the change in tension of the warp yarns Y which are unwound from a warp beam 2 and passed over a back roller 3 and then over said tension roller 1. This motion of the tension roller 1 is transmitted to a speed change control lever 7 of a speed change device or a speed reducer 6 through a link 5 which is articulated at one end thereof to the other end of the tension lever 4 and at the opposite end thereof to said control lever 7. The reduction unit 6, which reduces the output speed of a main motor M of the loom and drives the warp beam 2 at a reduced speed, thus changes its speed change ratio or reduction ratio in accordance with the displacement of the tension roller 1. In FIG. 1, reference symbol W denotes a counterweight which acts to urge the tension lever 4 to rotate in clockwise direction (as viewed in FIG. 1) about the shaft 30 for providing a desired tension to the warp yarns Y; reference numeral 8 designates the shaft of the beam 2; reference numeral 9 designates a shed formed by upper and lower sheets of warps Y.sub.1 and Y.sub.2 ; and numeral 10 indicates a cloth roller which is driven by the main motor through a reduction unit (not shown) for winding up at a constant speed a woven fabric or cloth C guided by a guide roller 11.
In the above arrangement for regulating warp yarn tension, when the tension of the warp yarns Y is increased to exceed the upper limit of a predetermined permissible range, the tension roller 1 is moved downwards against the action of the counterweight W to lift the speed change control lever 7 slightly, thereby increasing the speed at which the warp yarns Y are fed out from the warp beam 2; while, in the event of a decrease in warp yarn tension below the lower limit of said range, the tension roller 1 is displaced upwards under the influence of the counterweight W to turn the lever 7 slightly downward, thereby decreasing the warp yarn feeding speed.
In the above structure for warp yarn tension controlling, however, since the control lever 7 of the speed reduction unit 6 should be turned upwards for progressively increasing the rotational speed of the warp beam 2 with a progressive decrease in the diameter of the warp yarn winding on the warp beams 2 so as to maintain a substantially constant feeding speed of the warp yarns Y irrespective of the change in said diameter, the tension roller 1 will be moved downwards gradually, accordingly. Consequently, the direction in which the tension of warp yarns Y acts on the tension roller 1 is varied with the downward movement of the latter with the result that the balance in tension between the upper and lower sheets of warp yarns Y.sub.1, Y.sub.2 will be changed, thus posing a disadvantage in that the handle or woven density of the resulting fabric C may be badly affected.
There is another disadvantage in the above conventional method of warp yarn regulation when restarting the loom from its standstill state after a machine stop due to failure in weft insertion through a shed, or for replacement of the warp beam 2 with a new one. In the standstill state the tension roller 1 is placed far from a position corresponding to an optimum tension of the warp yarns Y. That is, because adjustment of the speed change ratio of the speed reduction unit 6 is made whenever the warp tension is thrown out of its permissible range and the amount of such adjustment may be excessively large, it not only takes a long time before the tension roller 1 resumes a position within its specified range corresponding to the permissible range of warp yarn tension, but also the tension roller 1 itself may begin an oscillating motion without being restored within the range, thus posing a fear of producing cloth C with so-called weaving bar, which degrades the fabric quality.
Furthermore, in the conventional method of warp yarn regulation which relies only on the position of the tension roller, adjustment for the regulation is made only after the warp yarn tension is thrown out of its allowable range, which means that the response of the control to compensate for excessively high or low warp yarn tension is not quick enough.